The invention relates in general to a system which evaluates air braked vehicles for verification of compliance with motor vehicle safety standards. More specifically, the system evaluates and tests service brake actuation and release timing, parking brake application timing, and performs general brake system troubleshooting.
Federal Motor Vehicle Safety Standard 121 (FMVSS 121) sets forth minimum braking system performance parameters with which all heavy duty vehicles such as straight trucks, buses, and combination vehicles including tractor-trailers, doubles, triples, and straight trucks with trailers must comply. Heavy duty vehicles typically utilize two separate braking systems: a service brake system and a parking brake system. The service brake system utilizes a brake pedal to apply and release the brakes during normal driving, and it permits the operator to slow or stop the vehicle. Parking brakes lock the wheels of a parked or unattended vehicle. The parking brakes are powerful mechanical spring brakes which are normally held open by air pressure, such that the springs engage the brakes when the pressure is released. To activate the parking brakes, the operator utilizes a manual control valve to release air pressure from the parking brake system. In addition, the parking brakes of an unhitched trailer are automatically engaged due to the release in air pressure as the trailer is uncoupled from the tractor""s supply air line.
The braking parameters specified by FMVSS 121 include service brake application timing, service brake release timing, and parking brake timing. Given an initial service brake reservoir pressure of 100 psi, service brake application timing is the time elapsed between the operator applying the brake pedal and the achievement of full braking pressure of 60 psi at all of the brake chambers under test. Service brake release timing is the time elapsed between the operator releasing the brake pedal, with 95 psi in all of the brake chambers, and the reduction of braking pressure to 5 psi at all of the brake chambers under test. An additional point is monitored if the vehicle under test is designed to tow an air brake equipped trailer. The additional monitoring point is located within a 50 cubic inch test reservoir which is temporarily connected to the trailer service brake line at the rear of the vehicle. In this case, the time elapsed until the achievement of full brake application pressure of 60 psi and braking pressure release of 5 psi at the test reservoir is also measured.
Given an initial supply air pressure of 100 psi, parking brake timing is the time elapsed between the operator activating the parking brake control valve or otherwise releasing the air from the system and the reduction of braking pressure to 3 psi at all of the chambers under test. Table 1 summarizes the service brake timing performance standards from FMVSS 121.
As a result of FMVSS 121, truck manufacturers and service centers which work on truck and trailer air brake systems need to be able to verify compliance with the performance standards. It is therefore an object of the invention to measure and graphically record the brake application and release timing of service air brake systems and the brake application timing of parking air brake systems. It is another object of the invention to provide a data acquisition system to perform other types of brake system diagnostic tests.
The present invention provides a brake response analysis system and a test method which measure and record brake pressure data representing the brake application and release timing of service brake systems and the brake application timing of parking brake systems. The brake pressure data are used to determine if a specific vehicle or item of motor vehicle equipment meets the minimum performance requirements of FMVSS 121. As a result, compliance with the service brake and parking brake timing with the parameters set forth in FMVSS 121 may be verified, and other brake system diagnostic tests may be performed.
In a preferred embodiment, the vehicular brake response analysis system includes an electronic control unit, a user interface, and sensors. The user interface and the sensors are coupled to the electronic control unit. The user interface is utilized to select a test methodology which is preferably a service timing test, a parking brake timing test, a dynamic balance test, a static balance test, a brake scan test, or a brake threshold test. A test start sensor which is coupled to the electronic control unit, senses commencement of a test time period, and provides a test start signal. At least one pressure sensor, which is coupled to the electronic control unit, is located at a monitoring point within a vehicular brake system, and the pressure sensor provides at least one pressure signal indicative thereof. The electronic control unit receives the test start and pressure signals, processes the signals according to a test methodology to determine if the performance of the vehicular brake system is within predetermined acceptable standards, and outputs at least one pressure signal to the user interface in graphical and numerical form.
In accordance with another preferred embodiment, the brake response analysis system includes a trailer test rig having a test rig switch and a pressure gauge. The trailer test rig is coupled to at least one of a trailer service brake system and a trailer parking brake system with an air line. The trailer test rig generates brake application and release test pressure for at least one of a trailer service brake system and a trailer parking brake system.
To perform a service brake application and release timing test, a pressure sensor is located at each vehicular service brake chamber. The test start sensor is at least one of a test rig switch and a brake pedal switch, the brake pedal switch is coupled to a vehicular brake pedal. The service brake application timing test measures a time period elapsed between an operator applying brake pressure, given a predetermined brake application start pressure in the service brake chambers, and the achievement of a predetermined brake application pressure at the service brake chambers. The service brake release timing test measures a time period elapsed between the operator releasing brake pressure, given a predetermined brake release start pressure in the service brake chambers, and the reduction of braking pressure to a predetermined brake release pressure at the service brake chambers.
To perform a parking brake timing test, a pressure sensor is located at each vehicular parking brake chamber. The test start sensor is at least one of a pressure transducer which is located at a supply air port on a vehicular parking brake control valve and a pressure transducer which is located within the air line which couples the trailer test rig to the trailer parking brake system. Given a predetermined initial supply air pressure, parking brake timing is the time elapsed between the operator activating the test start sensor by releasing the air from the system and the reduction of braking pressure to a predetermined parking brake release pressure at the parking brake chambers.